Communication node and communication system for performing clock synchronization

ABSTRACT

A communication system comprises a clock generator configured to generate a plurality of system clock signals used to synchronize components included in each of communication nodes in the communication system based on an external clock signal provided by an external clock source located outside the communication system and a physical layer configured to transmit any one of the generated system clock signals to a small cell communicatively connected to an end communication node of the communication system.

TECHNICAL FIELD

The present disclosure relates to a communication node and acommunication system for performing clock synchronization, and moreparticularly, to a communication node and a communication system capableof generating a plurality of system clock signals using an externalclock provided by an external clock source and controllingsynchronization of communication signals transmitted and receivedbetween an end communication node and a small cell based on any one ofthe generated system clock signals.

BACKGROUND ART

A distributed antenna system (DAS) is a system that may solve theproblem of communication shadow areas or high traffic concentration in aspecific area by spatially distributing a plurality of antennas.

The distributed antenna system is installed in buildings, tunnels,subways, etc. to provide communication services even to a shadow areawhere base transceiver station signals are difficult to reach. Thedistributed antenna system is also used to provide smooth services instadiums, large-sized facilities, and places where service demand ishigh.

Recently, in the distributed antenna system, there is an increasingdemand for transmission of Ethernet data or Internet Protocol (IP) dataas well as transmission of RF signals.

DESCRIPTION OF EMBODIMENTS Technical Problem

Provided are a communication node and a communication system forperforming clock synchronization capable of generating a plurality ofsystem clock signals using an external clock provided by an externalclock source and controlling synchronization of communication signalstransmitted and received between an end communication node and a smallcell based on any one of the generated system clock signals.

Solution to Problem

According to an aspect of an embodiments, a communication systemcomprising: a clock generator configured to generate a plurality ofsystem clock signals used to synchronize components included in each ofcommunication nodes in the communication system based on an externalclock signal provided by an external clock source located outside thecommunication system; and a physical layer configured to transmit anyone of the generated system clock signals to a small cellcommunicatively connected to an end communication node of thecommunication system.

According to an aspect of an embodiments, the communication system mayrelay at least one of an analog RF signal and a baseband digital signaltogether with at least one of Ethernet data and IP data.

According to an aspect of an embodiments, the baseband digital signalmay be a digital signal according to a standard of any one of CommonPublic Radio Interface (CPRI), Open Baseband Remote Radiohead Interface(OBSAI), Open Radio Interface (ORI), and eCPRI.

According to an aspect of an embodiments, the physical layer maycomprise an Ethernet physical layer, and the any one of the system clocksignals is transmitted to the small cell according to a synchronousEthernet (SyncE) standard.

According to an aspect of an embodiments, the external clock source maybe any one of a primary reference source (PRS), a primary referenceclock (PRC), a synchronization supply unit (SSU), stand-alonesynchronization equipment (SASE), a building integrated timing supply(BITS), an SDH equipment clock (SEC), a base station, and a GPS devicethat are located outside the communication system and communicativelyconnected to each other.

According to an aspect of an embodiments, the plurality of system clocksignals may comprise at least one of a first system clock signalcommonly used for synchronization of an RF processing part included inthe communication nodes in the communication system, a second systemclock signal commonly used for synchronization of an Ethernet processingpart included in the communication nodes, a third system clock signalcommonly used for synchronization of a main processing part included inthe communication nodes, and a fourth system clock signal commonly usedfor synchronization of a physical layer transceiver included in thecommunication nodes.

According to an aspect of an embodiments, the plurality of system clocksignals may be clock signals having different frequencies.

According to an aspect of an embodiments, the communication nodes in thecommunication system may be connected to each other through an opticallink.

According to an aspect of an embodiments, the any one of the systemclock signals may be a system clock signal having a frequency equal tothat of the second system clock signal.

According to an aspect of an embodiments, the end communication node ofthe communication system may be a remote device.

According to an aspect of an embodiments, the external clock may bereceived through a head-end device in the communication system.

According to an aspect of an embodiments, the clock generator may beincluded in the end communication node of the communication system, andgenerate the plurality of system clock signals using a clock recoveredfrom a communication signal which is transmitted from the head-enddevice and received at the end communication node after beingsynchronized based on the external clock.

According to an aspect of an embodiments, the external clock may bereceived directly at the end communication node in the communicationsystem.

According to an aspect of an embodiments, the clock generator may beincluded in the end communication node of the communication system andgenerate the plurality of system clock signals based on the directlyreceived external clock.

According to an aspect of an embodiments, a communication nodecomprising: a clock generator configured to generate a plurality ofsystem clock signals used to synchronize components included in thecommunication node based on an external clock provided by an externalclock source located outside the communication node or a communicationsignal received in synchronization with the external clock; and aphysical layer configured to transmit any one of the generated systemclock signals to a small cell communicatively connected to thecommunication node.

Advantageous Effects of Disclosure

Methods and devices according to an embodiment of the present disclosuremay generate a plurality of system clock signals using an external clockprovided by an external clock source and may effectively controlsynchronization of communication signals transmitted and receivedbetween an end communication node and a small cell based on any one ofthe generated system clock signals.

BRIEF DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a block diagram of a communication system according to anembodiment;

FIG. 2 is a block diagram according to an embodiment of a head-enddevice in FIG. 1;

FIG. 3 is a block diagram according to an embodiment of an extensiondevice in FIG. 1; and

FIG. 4 is a block diagram according to an embodiment of a remote devicein FIG. 1.

BEST MODE

The inventive concept may be variously modified and have variousembodiments, so that specific embodiments will be illustrated in thedrawings and described in the detailed description. However, this doesnot limit the inventive concept to specific embodiments, and it shouldbe understood that the inventive concept covers all the modifications,equivalents and replacements included within the idea and technicalscope of the inventive concept.

In describing the inventive concept, in the following description, adetailed explanation of known related technologies may be omitted toavoid unnecessarily obscuring the subject matter of the presentdisclosure. In addition, numeral figures (e.g., 1, 2, and the like) usedduring describing the specification are just identification symbols fordistinguishing one element from another element.

Further, in the specification, if it is described that one component is“connected” or “accesses” the other component, it is understood that theone component may be directly connected to or may directly access theother component but unless explicitly described to the contrary, anothercomponent may be “connected” or “access” between the components.

In addition, terms including “unit,” “er,” “or,” “module,” and the likedisclosed in the specification mean a unit that processes at least onefunction or operation and this may be implemented by hardware orsoftware such as a processor, a micro processor, a micro controller, acentral processing unit (CPU), a graphics processing unit (GPU), anaccelerated Processing unit (APU), a digital signal processor (DSP), anapplication specific integrated circuit (ASIC), and a field programmablegate array (FPGA) or a combination of hardware and software.Furthermore, the terms may be implemented in a form coupled to a memorythat stores data necessary for processing at least one function oroperation.

Moreover, it is intended to clarify that components in the specificationare distinguished in terms of primary functions of the components. Thatis, two or more components to be described below may be provided to becombined to one component or one component may be provided to be dividedinto two or more components for each more subdivided function. Inaddition, each of the respective components to be described below mayadditionally perform some or all functions among functions which othercomponents take charge of in addition to a primary function which eachcomponent takes charge of and some functions among the primary functionswhich the respective components take charge of are exclusively chargedby other components to be performed, of course.

A distributed antenna system according to an example embodiment of theinventive concept is a coverage system for an in-building service thattransmits voice communication and data communication with high qualityand seamlessness. It is also a system for servicing analog and digitaltelephone systems serviced in multiple bands with at least one antenna.

The distributed antenna system according to an embodiment of theinventive concept improves a poor propagation environment in a building,improves a poor received signal strength indication (RSSI) and theoverall reception sensitivity of a mobile terminal, chip energy/otherinterferences (Ec/Io), and provides a mobile communication service toevery corner of the building so that a user of the mobile communicationservice can freely talk anywhere in the building.

The distributed antenna system according to an embodiment of theinventive concept may support the mobile communication standard usedworldwide. For example, the distributed antenna system may support atime division duplex (TDD) service as well as a frequency divisionduplex (FDD) service, a very-high frequency (VHF), an ultra-highfrequency (UHF), and frequencies of 700 MHz, 800 MHz, 850 MHz, 900 MHz,1900 MHz, 2100 MHz, and 2600 MHz bands. Furthermore, the distributedantenna system may support a number of mobile communication standardssuch as a typical analog mobile communication service, that is, anadvanced mobile phone service (AMPS), digital time-division multipleaccess (TDMA), code-division multiple access (CDMA), widebandcode-division multiple access (WCDMA), high-speed downlink packet access(HSDPA), long-term evolution (LTE), LTE-advanced (LTE-A), 5G, and so on.

Hereinafter, embodiments of the inventive concept will be described indetail in turn.

FIG. 1 is a block diagram of a communication system according to anembodiment.

In FIG. 1, for convenience of description, a base transceiver station100-1, an IP network 100-2, a plurality of small cells 300 a to 300 dfor transmitting and receiving a communication signal through acommunication system 200 according to an embodiment of the presentdisclosure, and a network management server or a network managementsystem (NMS) 400 for managing the communication system 200 are showntogether.

The communication system 200 according to an embodiment may be referredto as a distributed antenna system (DAS).

Referring to FIG. 1, the communication system 200 may include a head-enddevice 210 that constitutes a head-end node and are communicativelyconnected to the base transceiver station (BTS) 100-1 and the IP network100-2, extension devices 220 a and 220 b constituting an extension node,and a plurality of remote devices 230 a, 230 b, 230 c, and 230 d whichconstitute a remote node and are connected to another remote node ordisposed at each service location of the remote to communicate with auser terminal.

According to an embodiment, the communication system 200 may relay atleast one of an analog RF signal and a baseband digital signal togetherwith at least one of Ethernet data and IP data.

According to an embodiment, the base station 100-1 may be a signalsource of the analog RF signal or the baseband digital signal relayed bythe communication system 200.

For example, the baseband digital signal may be a digital signalaccording to a standard of any one of Common Public Radio Interface(CPRI), Open Baseband Remote Radiohead Interface (OBSAI), Open RadioInterface (ORI), and eCPRI.

According to an embodiment, the communication system 200 may includesome components of the base station 100-1 or the IP network 100-2 or mayperform some functions of the base station 100-1 or the IP network100-2.

According to an embodiment, the base station 100-1 may be configured inplural.

Meanwhile, FIG. 1 shows an example of a topology of the communicationsystem 200 and various variations are possible in the communicationsystem 200 considering specificity of installation areas and applicationfields (e.g., in-building, a subway, a hospital, a stadium, etc.). Forexample, the number of the head-end device 210, the extension devices220 a and 220 b, and the remote devices 230 a, 230 b, 230 c, and 230 d,and a connection relationship between upper and lower ends thereof maybe different from FIG. 1.

In the present specification, the term “end communication node of acommunication system” may mean a node that processes and transmits acommunication signal last in a communication system.

According to an embodiment, the extension devices 220 a and 220 b in thecommunication system 200 may be utilized when the number of branches ofthe head-end device 210 is limited compared to the number of remotedevices that need to be installed.

Each node in the communication system 200 and its functions will bedescribed in more detail. First, the head-end device 210 may interfacewith the base station 100-1 and the IP network 100-2.

According to an embodiment, the head-end device 210 may be connected toa plurality of base stations.

According to an embodiment, the head-end device 210 may be implementedas a main head-end device and a sub head-end device, and may beconnected to a base station for each service frequency band of aspecific service provider or a base station for each sector. In somecases, the main head-end device may compensate for coverage by the subhead-end device.

The head-end device 210 may selectively transmit at least one of ananalog RF signal and a baseband digital signal received from the basestation 100-1, and at least one of Ethernet data and IP data receivedfrom the IP network 100-2 to the extension device 220 a or the remotedevice 230 a.

According to an embodiment, the head-end device 210 may combine at leastone of the analog RF signal and the baseband digital signal receivedfrom the base station 100-1 and at least one of the Ethernet data andthe IP data received from the IP network 100-2 to transmit the combinedsignal to the extension device 220 a or the remote device 230 a.

According to another embodiment, the head-end device 210 may directlyreceive and process a baseband signal from the base station 100-1.

Detailed structure and operation of the head end device 210 will bedescribed later with reference to FIG. 2.

The extension device 220 a may transmit the received signal to theremote device 230 c connected to the extension device 220 a.

The extension device 220 b is connected to one end of the remote device230 a and may receive a signal received from the head-end device 210through the remote device 230 a in downlink communication. The extensiondevice 220 b may transmit the received signal back to the remote device230 d connected to a rear end of the extension device 220 b.

Each of the remote devices 230 a, 230 b, 230 c, and 230 d may performsignal processing such as separating, amplifying, and transmitting ofthe analog RF signal or the baseband digital signal included in thereceived signal for each frequency band. Accordingly, each of the remotedevices 230 a, 230 b, 230 c, and 230 d may transmit a base stationsignal to a user terminal in its service coverage through a serviceantenna (not shown).

The remote devices 230 a, 230 b, 230 c, and 230 d may transmit Ethernetdata or IP data included in the received signal to the small cells 300a, 300 b, 300 c, and 300 d that are communicatively connected to theremote devices 230 a, 230 b, 230 c, and 230 d, respectively.

Each of the remote devices 230 a, 230 b, 230 c, and 230 d, together withthe Ethernet data or the IP data, may transmit any one of system clocksignals used in the communication system 200 to the small cells 300 a,300 b, 300 c, and 300 d, respectively.

According to an embodiment, the remote device 230 a and the remotedevice 230 b, and the remote device 230 c and the remote device 230 cmay be connected to each other through an optical link or an RF cable,and a plurality of remote devices may be connected to each other in acascade structure if necessary.

At a lower end of the head-end device 210, the head-end device 210, theextension devices 220 a and 220 b, and the remote devices 230 a, 230 b,230 c, and 230 d may be connected to each other through the opticallink, but a signal transport medium or a communication method betweeneach node may vary.

For example, at least one of the head-end device 210 and the extensiondevice 220 a, the head-end device 210 and the remote device 230 a, andthe extension devices 220 a and 220 b and the remote device 230 c and230 d may be connected to each other through an RF cable, a twistedcable, a UTP cable or the like in addition to the optical cable.

Therefore, in the communication system 200, the head-end device 210, theextension devices 220 a and 220 b, and the remote devices 230 a, 230 b,230 c, and 230 d may include an optical transceiver module fortransmitting and receiving optical signals through electro-opticalconversion/photoelectric conversion, and may further include awavelength division multiplexing (WDM) device when nodes are connectedto each other by a single optical cable.

The small cells 300 a, 300 b, 300 c, and 300 d may be communicativelyconnected to a rear end of each of the remote devices 230 a, 230 b, 230c, and 230 d, respectively.

According to an embodiment, the remote devices 230 a, 230 b, 230 c, and230 d and the small cells 300 a, 300 b, 300 c, and 300 d may communicatewith each other, respectively, according to a synchronous Ethernet(SyncE) standard.

In the present specification, the term “small cell” may broadly mean asmall base station, and may collectively refer to a cell covering anarrow range such as small output base station equipment, a picocell, afemtocell, and a metrocell, and the small cell may support heterogeneouscommunication such as Wi-Fi.

The communication system 200 may be connected to an external managementdevice (not shown) such as a network management server or a networkmanagement system (NMS) 300, a network operation center (NOC) (notshown), and the like via a network. Accordingly, an administrator mayremotely monitor the status and problem of each node of thecommunication system 200, and may remotely control the operation of eachnode.

FIG. 2 is a block diagram according to an embodiment of the head-enddevice 210 in FIG. 1.

Referring to FIGS. 1 and 2, the head-end device 210 may include an RFprocessing part 2110, a main processing part 2120, a physical layertransmitter 2131, a physical layer receiver 2132, an Ethernet processingpart 2140, a local clock 2151, a clock switch 2153, and a clockgenerator 2154.

The RF processing part 2110 is a part for processing an RF signaltransmitted and received with the base station 100-1 or a signal (analogsignal or digital signal) generated based on the RF signal.

According to an embodiment, the RF processing part 2110 may transmit andreceive an analog RF signal or a baseband digital signal with the basestation 100-1.

The RF processing part 2110 may include a receiver 2111, a firstinterface circuit 2112, an analog-to-digital converter 2113, adigital-to-analog converter 2114, a second interface circuit 2115, atransmitter 2116, and a synchronization controller 2117.

In downlink communication, the receiver 2111 may receive a downlinksignal received from the base station 100-1 and transmit the downlinksignal to the first interface circuit 2112.

The first interface circuit 2112 may interface the downlink signalreceived from the receiver 2111. According to an embodiment, the firstinterface circuit 2112 may interface the received downlink signal to beprocessed in the communication system 210 by adjusting the power of thereceived downlink signal or down-converting frequencies.

The analog-to-digital converter 2113 may output a digital signal byanalog-to-digital converting the downlink signal interfaced through thefirst interface circuit 2112.

According to an embodiment, when the receiver 2111 receives a digitalsignal from the base station 100-1, the analog-to-digital converter 2113may not be included in the RF processing part 2110.

In uplink communication, the digital-to-analog converter 2114 maydigital-to-analog convert an uplink signal to output an analog signal.

According to an embodiment, when the transmitter 2116 transmits adigital signal to the base station 100-1, the digital-to-analogconverter 2114 may not be included in the RF processing part 2110.

The second interface circuit 2115 may interface an uplink signal outputby the digital-to-analog converter 2114. According to an embodiment, thesecond interface circuit 2115 may process the uplink signal to betransmitted to the base station 100-1 by adjusting the power of theuplink signal or up-converting frequencies.

The transmitter 2116 may transmit the uplink signal interfaced by thesecond interface circuit 2115 to the base station 100-1.

The synchronization controller 2117 may control synchronization of eachof the components (2111 to 2116) in the RF processing part 2110 based onany one of a plurality of system clock signals generated by the clockgenerator 2154.

The main processing part 2120 distributes or branches uplink signalstransmitted by combining different types of signals transmitted throughthe head-end device 210, or selects or combines different types ofdownlink signals and transmits them.

The main processing part 2120 may include a multiplexer 2121, a buffer2122, a recovery circuit 2123, a demultiplexer 2124, and asynchronization controller 2125.

In downlink communication, the multiplexer 2121 may receive differenttypes of downlink signals and select and output any one of the receiveddownlink signals.

According to an embodiment, the multiplexer 2121 may combine differenttypes of downlink signals to output the combined downlink signal.

According to an embodiment, the different types of downlink signals mayinclude downlink signals received from the RF processing part 2110 anddownlink signals received from the Ethernet processing part 2140.

The buffer 2122 may buffer and output a downlink signal output from themultiplexer 2121.

According to an embodiment, the buffer 2122 may be implemented as afan-out buffer.

In uplink communication, the recovery circuit 2123 may recover clocksignals and data contained in an uplink signal received from physicallayer receiver 2132.

The demultiplexer 2124 may distribute or branch different types ofuplink signals included in an uplink signal received through thereconstruction circuit 2123, and may transmit the distributed orbranched uplink signals to the RF processing part 2110 and the Ethernetprocessing part 2140, respectively.

The synchronization controller 2125 may control synchronization of eachof the components (2121 to 2124) in the main processing part 2120 basedon any one of the plurality of system clock signals generated by theclock generator 2154.

The physical layer transmitter 2131 may receive a downlink signalprocessed and output by the main processing part 2120 and a system clocksignal generated by the clock generator 2154. For example, the systemclock signal may be a clock signal commonly used for synchronization ofa physical layer transceiver.

The physical layer transmitter 2131 may transmit the received downlinksignal to the outside of the head-end device 210 by synchronizing withthe received system clock signal. The signal output from the physicallayer transmitter 2131 may be transmitted to the remote device 230 a orthe extension device 220 a connected to the head-end device 210.

The physical layer receiver 2132 may receive an uplink signal receivedby the head-end device 210 and a system clock signal generated by theclock generator 2154. For example, the system clock signal may be aclock signal commonly used for synchronization of a physical layertransceiver.

The physical layer receiver 2132 may transmit the received uplink signalto the main processing part 2120 in synchronization with the receivedsystem clock signal.

The Ethernet processing part 2140 processes Ethernet data or IP datatransmitted and received with the IP network 100-2, or processedEthernet data or processed IP data.

The Ethernet processing part 2140 may include an Ethernet physical layer2141, an Ethernet switch 2142, and a synchronization controller 2143.

The Ethernet physical layer 2141 may interface the Ethernet data or theIP data transmitted and received with the IP network 100-2.

The Ethernet switch 2142 may switch a signal path in downlinkcommunication or uplink communication of the Ethernet processing part2140.

In downlink communication, the Ethernet switch 2142 may transmitEthernet data or IP data received from the Ethernet physical layer 2141to the main processing part 2120.

In uplink communication, the Ethernet switch 2142 may transmit Ethernetdata or IP data received from the main processing part 2120 to theEthernet physical layer 2141.

The synchronization controller 2143 may control synchronization of eachof the components (2141 to 2142) in the Ethernet processing part 2140based on any one of the plurality of system clock signals generated bythe clock generator 2154.

The local clock 2151 may autonomously generate a clock in the head-enddevice 210. According to an embodiment, the local clock 2151 may beimplemented by including a combination of an oscillation circuit andcrystals or a local oscillator.

An external clock source 2152 may be located outside the head-end device210 or outside the communication system 200 to be communicativelyconnected to the head-end device 210 and may provide an external clock.

According to an embodiment, the external clock source 2152 may beimplemented as any one of a primary reference source (PRS), a primaryreference clock (PRC), a synchronization supply unit (SSU), stand-alonesynchronization equipment (SASE), a building integrated timing supply(BITS), an SDH equipment clock (SEC), a base station, and a GPS device.

The clock switch 2153 may select one of an internal clock signalgenerated by the local clock 2151 and an external clock signal inputfrom the external clock source 2152, and may transmit the selected clocksignal to the clock generator 2154.

According to an embodiment, the clock switch 2153 basically transmitsthe external clock signal input from the external clock source 2152 tothe clock generator 2154, but may transmit the internal clock signalgenerated by the local clock 2151 to the clock generator 2154 when asynchronization loss occurs.

The clock generator may generate a plurality of system clock signalsused to synchronize components included in each of communication nodesin the communication system 200 based on the internal clock signal orthe external clock signal received from the clock switch 2153.

According to an embodiment, the plurality of system clock signals mayinclude at least one of a first system clock signal commonly used forsynchronization of an RF processing part (e.g., 2110), a second systemclock signal commonly used for synchronization of an Ethernet processingpart (e.g., 2140), a third system clock signal commonly used forsynchronization of a main processing part (e.g., 2120), and a fourthsystem clock commonly used for synchronization of a physical layertransceivers (e.g., 2131 and 2132).

According to an embodiment, the first system clock signal, the secondsystem clock signal, the third system clock signal, and the fourthsystem clock signal may be clock signals having different frequencies.

FIG. 3 is a block diagram according to an embodiment of the extensiondevice 220 a in FIG. 1.

Referring to FIGS. 1 to 3, the extension device 220 a may include anupper physical layer transceiver 2201, a main processor 2202, aplurality of lower physical layer transceivers 2203-1 to 2203-n, and arecovery circuit 2204, a local clock 2205, a clock switch 2206, and aclock generator 2207.

The upper physical layer transceiver 2201 may transmit and receive anuplink signal or a downlink signal with the head-end device 210 througha physical layer.

According to an embodiment, the upper physical layer transceiver 2201may synchronize an uplink signal or a downlink signal with a systemclock signal generated by the clock generator 2207, and may transmit andreceive the synchronized signal with the head-end device 210.

According to an embodiment, the system clock signal may be a clocksignal commonly used for synchronization of a physical layer transceiver(e.g., 2131 and 2132 of FIG. 2).

In the case of the extension device 220 a having the remote device 230 aconnected to an upper end, the upper physical layer transceiver 2201 maytransmit and receive an uplink signal or a downlink signal with theremote device 230 a through a physical layer.

The main processor 2202 may perform overall signal processing in theextension device 220 a. The main processor 2202 may distribute adownlink signal received from the upper end to the plurality of lowerphysical layer transceivers 2203-1 to 2203-n, or may combine or switchuplink signals received through the plurality of lower physical layertransceivers 2203-1 to 2203-n to transmit to the upper physical layertransceiver 2201.

According to an embodiment, the main processor 2202 may controlsynchronization of the main processor 2202 based on any one of aplurality of system clock signals generated by the clock generator 2207.

For example, the system clock signal may be a clock signal commonly usedfor synchronization of a main processing part (e.g., 2120 of FIG. 2).

The plurality of lower physical layer transceivers 2203-1 to 2203-n maybe connected to remote devices (e.g., 230 c) connected to a lower end ofthe extension device 220 a, respectively, and may transmit and receivean uplink signal or a downlink signal with the remote devices (e.g., 230c) connected to the lower end of the extension device 220 a through aphysical layer.

According to an embodiment, each of the plurality of lower physicallayer transceivers 2203-1 to 2203-n synchronizes an uplink signal or adownlink signal with the system clock signal generated by the clockgenerator 2207, and may transmit and receive the synchronized signalwith each of remote devices (e.g., 230 c) connected to the lower end ofthe extension device 220 a.

According to an embodiment, the system clock signal may be a clocksignal commonly used for synchronization of a physical layer transceiver(e.g., 2131 and 2132 of FIG. 2).

The recovery circuit 2204 may recover clock signals and data included ina downlink signal or an uplink signal received from the upper physicallayer transceiver 2201.

The local clock 2205 may autonomously generate a clock in the extensiondevice 220 a. According to an embodiment, the local clock 2205 may beimplemented by including a combination of an oscillator and crystals ora local oscillator.

The clock switch 2206 may select one of an internal clock signalgenerated by the local clock 2205 and a clock signal recovered by therecovery circuit 2204, and may transmit the selected clock signal to theclock generator 2207.

According to an embodiment, the clock switch 2206 basically transmitsthe clock signal recovered by the recovery circuit 2204 to the clockgenerator 2207, but may transmit the internal clock signal generated bythe local clock 2205 to the clock generator 2207 when a synchronizationloss occurs.

The clock generator 2207 may generate a plurality of system clocksignals used to synchronize components in the extension device 220 abased on the internal clock signal or the recovered clock signalreceived from the clock switch 2206.

According to an embodiment, the plurality of system clock signals mayinclude at least one of a third system clock signal commonly used forsynchronization of a main processing part (e.g., 2120 of FIG. 2 or 2202of FIG. 3), and a fourth system clock signal commonly used forsynchronization of a physical layer transceiver (e.g., 2131 and 2132 ofFIG. 2 or 2201 and 2203-1 to 2203-n of FIG. 3).

The extension device 220 b illustrated in FIG. 1 may be implemented insubstantially the same structure as the extension device 220 aillustrated in FIG. 3, and only a configuration corresponding to anobject that transmits and receives signals at both ends may be changed.

FIG. 4 is a block diagram according to an embodiment of the remotedevice in FIG. 1.

Referring to FIGS. 1 to 4, the remote device 230 may include an upperphysical layer transceiver 2301, a main processor 2302, a lower physicallayer transceiver 2303, an RF processing part 2310, an antenna 2320, anEthernet physical layer 2330, a recovery circuit 2342, a local clock2343, a clock switch 2344, a clock generator 2346, and a timingcontroller 2347.

The upper physical layer transceiver 2301 may transmit and receive anuplink signal or a downlink signal with the extension device 220 athrough a physical layer.

According to an embodiment, the upper physical layer transceiver 2301may synchronize an uplink signal or a downlink signal with a systemclock signal generated by the clock generator 2346, and may transmit andreceive the synchronized signal with the extension device 220 a.

According to an embodiment, the system clock signal may be a clocksignal commonly used for synchronization of a physical layer transceiver(e.g., 2131 and 2132 of FIG. 2 or 2201 and 2203-1 to 2203-n of FIG. 3).

The main processor 2302 may perform overall signal processing in theremote device 230 c.

The main processor 2302 may distribute a downlink signal received froman upper node of the remote device 230 c to each of the lower physicallayer transceiver 2303, the RF processing part 2310, and the Ethernetphysical layer 2330, or may combine or switch received uplink signals totransmit to the upper physical layer transceiver 2301.

According to an embodiment, the main processor 2302 may controlsynchronization of the main processor 2302 based on any one of systemclock signals generated by the clock generator 2348.

For example, the system clock signal may be a clock signal commonly usedfor synchronization of a main processing part (e.g., 2120 of FIG. 2 or2202 of FIG. 3).

The lower physical layer transceiver 2303 may be included when a remotedevice (not shown) is daisy chained to a lower end of the remote device230 c, and may transmit and receive an uplink signal or a downlinksignal with a remote device connected through a physical layer.

The RF processing part 2310 may process an RF signal (or digitized RFsignal) distributed from the main processor 2302 in downlinkcommunication and transmit the RF signal to terminals through theantenna 2320, or may process and transmit an RF signal received from theterminals in uplink communication to the main processor 2302.

According to an embodiment, the RF processing part 2310 may transmit andreceive an RF signal with the terminals through the antenna 2320.

The RF processing part 2310 may include a digital-to-analog converter2311, a first interface circuit 2312, an RF transmitter 2313, an RFreceiver 2314, a second interface circuit 2315, an analog-to-digitalconverter 2316, and a synchronization controller 2317.

In downlink communication, the digital-to-analog converter 2311 mayconvert a digital downlink signal received from the main processor 2302into an analog downlink signal and output the analog downlink signal.

The first interface circuit 2312 may interface the analog downlinksignal output from the digital-to-analog converter 2311. According to anembodiment, the first interface circuit 2312 may process the analogdownlink signal to be transmitted through the antenna 2320 by adjustingthe power of the analog downlink signal or by up-converting frequencies.

The RF transmitter 2313 may transmit a downlink signal in the form of anRF signal through the antenna 2320.

In uplink communication, the RF receiver 2314 may receive an uplinksignal in the form of an RF signal through the antenna 2320.

The second interface circuit 2315 may interface an analog uplink signaloutput from the RF receiver 2314. According to an embodiment, the secondinterface circuit 2315 may interface the analog uplink signal to beprocessed in the communication system 210 by adjusting the power of theanalog uplink signal or down-converting frequencies.

The analog-to-digital converter 2316 may convert an analog uplink signaloutput from the second interface circuit 2315 into a digital uplinksignal and output the digital uplink signal.

The synchronization controller 2317 may control synchronization of eachof the components (2311 to 2316) in the RF processing part 2310 based onany one of system clock signals generated by the clock generator 2346.

For example, the system clock signal may be a clock signal commonly usedfor synchronization of an RF processing part (e.g., 2110 of FIG. 2).

An Ethernet physical layer transceiver 2330 may process Ethernet data(or IP data) distributed from the main processor 2302 in downlinkcommunication and transmit the processed Ethernet data (or IP data) toterminals through the small cell 300 c, and may process the Ethernetdata (or IP data) received from the terminals through the small cell 300c in uplink communication and transmit the processed Ethernet data (orIP data) to the main processor 2302.

The Ethernet physical layer transceiver 2330 may be synchronized underthe control of the timing controller 2347 based on the any one of thesystem clock signals generated by the clock generator 2346.

According to an embodiment, the Ethernet physical layer transceiver 2330may transmit the any one of the system clock signals generated by theclock generator 2346 to a connected small cell (e.g., 300 c).

For example, the system clock signal may be a clock signal commonly usedfor synchronization of an Ethernet processing part (e.g., 2140 of FIG.2).

According to an embodiment, the Ethernet physical layer transceiver 2330may transmit the any one of the system clock signals to a small cell(e.g., 300 c) according to a synchronous Ethernet (SyncE) standard.

The recovery circuit 2342 may recover clock signals and data included inthe downlink signal or the uplink signal received from the upperphysical layer transceiver 2301.

The local clock 2205 may autonomously generate a clock in the remotedevice 230 c. According to an embodiment, the local clock 2343 may beimplemented by including a combination of an oscillator and crystals ora local oscillator.

The clock switch 2344 may select one of an internal clock signalgenerated by the local clock 2343 and a clock signal recovered by therecovery circuit 2342, and may transmit the selected clock signal to theclock generator 2346.

According to an embodiment, the clock switch 2344 basically transmitsthe clock signal recovered by the recovery circuit 2342 to the clockgenerator 2346, but may transmit the internal clock signal generated bythe local clock 2343 to the clock generator 2346 when a synchronizationloss occurs.

The clock generator 2346 may generate a plurality of system clocksignals used to synchronize components in the remote device 230 c basedon the internal clock signal or the recovered clock signal received fromthe clock switch 2344.

According to an embodiment, the plurality of system clock signals mayinclude at least one of a first system clock signal commonly used forsynchronization of an RF processing part (e.g., 2110 of FIG. 2 or 2310of FIG. 4), a second system clock signal commonly used forsynchronization of an Ethernet processing part (e.g., 2140 of FIG. 2 or2330 of FIG. 4), a third system clock signal commonly used forsynchronization of a main processing part (e.g., 2120 of FIG. 2, 2202 ofFIG. 3, or 2302 of FIG. 4), and a fourth system clock signal commonlyused for synchronization of a physical layer transceiver (e.g., 2131 and2132 of FIGS. 2, 2201 and 2203-1 to 2203-n of FIG. 3, or 2301 and 2303of FIG. 4).

The remote devices 230 a to 230 d illustrated in FIG. 1 may beimplemented in substantially the same structure as the remote device 230c illustrated in FIG. 3, and only a configuration corresponding to anobject that transmits and receives signals at both ends may be changed.

While the present disclosure has been particularly shown and describedwith reference to embodiments thereof, it will be understood thatvarious changes in form and details may be made therein withoutdeparting from the spirit and scope of the following claims.

The invention claimed is:
 1. A communication system comprising: a clockgenerator configured to generate a plurality of system clock signalsused to synchronize components included in each of communication nodesin the communication system based on an external clock signal providedby an external clock source located outside the communication system;and a physical layer configured to transmit any one of the generatedsystem clock signals to a small cell communicatively connected to an endcommunication node of the communication system, wherein the plurality ofsystem clock signals include at least one of: a first system clocksignal commonly used for synchronization of a radio frequency (RF)processing part included in the communication nodes in the communicationsystem, a second system clock signal commonly used for synchronizationof an Ethernet processing part included in the communication nodes, athird system clock signal commonly used for synchronization of a mainprocessing part included in the communication nodes, and a fourth systemclock signal commonly used for synchronization of a physical layertransceiver included in the communication nodes.
 2. The communicationsystem of claim 1, the communication system capable of relaying at leastone of an analog RF signal and a baseband digital signal together withat least one of Ethernet data and IP data.
 3. The communication systemof claim 2, wherein the baseband digital signal is a digital signalaccording to a standard of any one of Common Public Radio Interface(CPRI), Open Baseband Remote Radiohead Interface (OBSAI), Open RadioInterface (ORI), and eCPRI.
 4. The communication system of claim 1,wherein the physical layer comprises an Ethernet physical layer, and theany one of the system clock signals is transmitted to the small cellaccording to a synchronous Ethernet (SyncE) standard.
 5. Thecommunication system of claim 1, wherein the external clock source isany one of a primary reference source (PRS), a primary reference clock(PRC), a synchronization supply unit (SSU), stand-alone synchronizationequipment (SASE), a building integrated timing supply (BITS), an SDHequipment clock (SEC), a base station, and a GPS device that are locatedoutside the communication system and communicatively connected to eachother.
 6. The communication system of claim 1, wherein the plurality ofsystem clock signals are clock signals having different frequencies. 7.The communication system of claim 1, wherein the communication nodes inthe communication system are connected to each other through an opticallink.
 8. The communication system of claim 1, wherein the any one of thesystem clock signals is a system clock signal having a frequency equalto that of the second system clock signal.
 9. The communication systemof claim 1, wherein the end communication node of the communicationsystem is a remote device.
 10. The communication system of claim 1,wherein the external clock signal is received through a head-end devicein the communication system.
 11. The communication system of claim 10,wherein the clock generator is included in the end communication node ofthe communication system, and generates the plurality of system clocksignals using a clock signal recovered from a communication signal whichis transmitted from the head-end device and received at the endcommunication node after being synchronized based on the external clocksignal.
 12. The communication system of claim 1, wherein the externalclock signal is received directly at the end communication node in thecommunication system.
 13. The communication system of claim 12, whereinthe clock generator is included in the end communication node of thecommunication system and generates the plurality of system clock signalsbased on the directly received external clock.
 14. A communication nodecomprising: a clock generator configured to generate a plurality ofsystem clock signals used to synchronize components included in thecommunication node based on an external clock provided by an externalclock source located outside the communication node or a communicationsignal received in synchronization with the external clock; and aphysical layer configured to transmit any one of the generated systemclock signals to a small cell communicatively connected to thecommunication node, wherein the plurality of system clock signalsinclude at least one of: a first system clock signal commonly used forsynchronization of a radio frequency (RF) processing part included inthe communication nodes in the communication system, a second systemclock signal commonly used for synchronization of an Ethernet processingpart included in the communication nodes, a third system clock signalcommonly used for synchronization of a main processing part included inthe communication nodes, and a fourth system clock signal commonly usedfor synchronization of a physical layer transceiver included in thecommunication nodes.